Lithium batteries are prepared from one or more lithium electrochemical cells. Such cells have included an anode (negative electrode), of metallic lithium, a cathode (positive electrode) typically a transition metal chalcogenide, and an electrolyte interposed between electrically insulated, spaced-apart, positive and negative electrodes. The electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous (aprotic) organic solvents. By convention, during discharge of the cell, the negative electrode of the cell is defined as the anode. During use of the cell, lithium ions (Li+) are transferred to the negative electrode on charging. During discharge, lithium ions (Li+) are transferred from the negative electrode (anode) to the positive electrode (cathode). Upon subsequent charge and discharge, the lithium ions (Li+) are transported between the electrodes. Cells having metallic lithium anode and metal chalcogenide cathode are charged in an initial condition. During discharge, lithium ions from the metallic anode pass through the liquid electrolyte to the electrochemically active material of the cathode whereupon electrical energy is released. During charging, the flow of lithium ions is reversed and they are transferred from the positive electrode active material through the ion conducting electrolyte and then back to the lithium negative electrode.
The lithium metal anode has been replaced with a carbon anode, that is, a carbonaceous material such as non-graphitic amorphous coke, graphitic carbon, or graphites, which are intercalation compounds. This presents a relatively advantageous and safer approach to rechargeable lithium as it replaces lithium metal with a material capable of reversibly intercalating lithium ions, thereby providing the "rocking chair" battery in which lithium ions "rock" between the intercalation electrodes during the charging/discharging/recharging cycles. Such lithium metal free cells may thus be viewed as comprising two lithium ion intercalating (absorbing) electrode "sponges" separated by a lithium ion conducting electrolyte, usually comprising a lithium salt dissolved in nonaqueous solvent or a mixture of such solvents. Numerous such electrolytes, salts, and solvents are known in the art. Such carbon anodes may be prelithiated prior to assembly within the cell having the cathode intercalation material. Since anode prelithiation is difficult, it is more common to have the lithium contained in the positive electrode. Lithium metal chalcogenide materials such as lithium manganese oxide, lithium nickel oxide and lithium cobalt oxide are common positive electrode active materials. Among these, lithium manganese oxide is preferred.
Methods of synthesis for Li.sub.1 Mn.sub.2 O.sub.4 compounds are known and are reactions generally between stoichiometric quantities of a lithium containing compound and a manganese containing compound, exemplified by a lithium salt and manganese oxide. See Hunter, U.S. Pat. No. 4,246,253. However, such compounds prepared by conventional methods have a disadvantage in that the charge capacity of a cell comprising a cathode of such compounds suffers a progressive loss in capacity as the number of cycles of such cell increases. That is, although the initial capacity may be an acceptable value, such initial capacity value is diminished upon the first cycle of operation and such capacity further diminishes on every successive cycle of operation. Such capacity fading is well known.
In U.S. Pat. No. 4,828,834, Nagaura, et al, attempted to reduce capacity fading by sintering precursor lithium and manganese materials and thereby forming an LiMn.sub.2 O.sub.4 intercalation compound. However, Nagaura's LiMn.sub.2 O.sub.4 compounds were not fully crystallized spinel electrodes and suffered from a very low capacity. Similar to Nagaura, Tarascon, U.S. Pat. No. 5,425,932, shows a process for producing lithium manganese oxide which requires heating precursors in an evacuated, sealed ampoule. The cooling occurs at a very slow rate over a period of 4 to 6 days, using strictly controlled conditions, while the ampoule remains sealed. The complexity of this process and the control required are self-evident.
Despite the above approaches, there remains the difficulty of obtaining lithium manganese oxide (LMO) based electrode materials having the attractive capacity of the basic spinel Li.sub.1 Mn.sub.2 O.sub.4 intercalation compound, but without its disadvantage of significant capacity loss on progressive cycling. Therefore, what is needed is a new electrode active material. There is also needed a new process for preparing electrode active material which is economical and adaptable to commercial production processes and achieves good conversion of the starting materials to the final desired product.